Horseshoe crab (Modern Animal) >>
Trilobite, meaning three lobes or parts is currently the most likely ancestor of the Horseshoe crab. They are a series of hard shelled arthropods and in this case the species Asaphiscus wheeleri will be studied. This case study will attempt to explain the reasons behind the extinction of the Asapiscus wheeleri as well as its habitat and adaptations.
General Information
Scientific Classification
Level
Classification
Kingdom
Animalia
Phylum
Arthopoda
Class
Trilobita
Order
Ptychopariida
Family
Asaphiscidae
Genus
Asaphicus
Species
Wheeleri
Trilobite
Habitat
Ancient World (Cambrian)
The Asapiscus wheeleri existed during the Cambrian age, a time when the land masses were mostly still similar to Pangaea. Fig. 02 demonstrates an artist’s impression of what the world most probably looked like during the Cambrian age. The highlighted section (bright green) shows the most probably location of where the Trilobite lived, based on location of current fossils. During this time, the general Earth was warmer than today with and was a period when under-sea creatures flourished.
Cambrian was also a time when there was one of the most diverse amounts of trilobites, which accounted for almost half of all known hard-shelled marine creatures of the time. The Asaphiscus wheeleri fossils which have been located in the United States (Central) demonstrates as said before, the probable location of where the Asapiscus wheeleri lived.
The local flora of the sea was extremely diverse, with a great number of seaweeds and other aquatic plants. This meant that the brownish trilobite’s colour and its descendant, the horse-shoe crab, may have adapted to this murky colour as a means of protecting itself from predators. Apart from the flora, aquatic fauna was also at it’s height with a greatly diverse number of sea creatures including the trilobites diet, thought to be smaller crustaceans, molluscs and other species of Trilobite.
It can be said that their habitat animals is equal to that of the Horseshoe crab. However, unlike the Horseshoe crab, which has almost no predators, the Asaphiscus wheeleri was an extremely good lunch for animals such as the Laggania cambria (fig. 3) or even one of the largest sea creatures, the Eurypterid, ancient four metre sea scorpions.
Ancient Cambrian Habitat
During the Cambrian period, the temperatures would have generally been wetter and drier than today, meaning that there would have been more storms both on land and at sea. This may not have been exceptionally good for the trilobite Asapiscus wheeleri as it had a relatively small tail for balance. It could have meant that the Asapiscus wheeleri would be flipped over and easily devoured by other predators. This climate also meant most probably that the Trilobite, instead of depositing its young on land, composed of mostly barren desert, would have chosen the wetter marshes with large plantations of flora as camouflage.
Adaptations
Structural Adaptation One
Compared to the Horseshoe crab, the Asapiscus wheeleri had a heavier exoskeleton made from calcium minerals. This exoskeleton would require changing or replacement as the Trilobite grew and this process would involve splitting the exoskeleton through the head and thorax in a process called moulting. Such a heavy exoskeleton is most beneficial for the animal because of the great number of large predators which the Asapiscus wheeleri had to protect itself from.
The most likely environmental pressure which gave rise to a tough hard exoskeleton would have most likely been the great number of predators during the Cambrian age. Although it may have slowed down the swimming speed of the Asapiscus wheeleri, there must have been more chance of it surviving an attack due to its tough shell as a pose to outrunning the large predators. It is also thought that the earliest trilobites had a softer shell and, in an attempt to ensure survival, natural selection pushed for the development of this harder exoskeleton.
Structural Adaptation Two
Another structural adaptation of the Trilobite is the uniquely complex compound eyes. These complex compound eyes are extremely unique as there are no other known records of animal eyes composed from calcite. However, these eyes are similar to other animals such as cheetahs or other vertebrates. This is so because these compound eyes also have complex lenses which are able to detect colour and movement, unlike the Horseshoe crab. These eyes were thought to be used for three main purposes:
To be able to detect predators in the earliest instance in order to escape.
To be able to hunt and see prey before other competitors.
To be able to search for mates, again due to high numbers of competitors.
It is thought by scientists that this compound eye was conceived as a result of sudden rapid development of animals during the Cambrian age. As a result, this became an environmental pressure for animals to hunt with many competitors as well as run from many predators and therefore led to the development of these eyes.
Behavioural Adaptation One
A very interesting behaviour of the Trilobite is the fact that it sometimes hides in caverns when scavenging, a juvenile or moulting. The reason which scientist most attribute to this particular behaviour is that these are often times when the Asapiscus wheeleri is most vulnerable. When moulting, the exoskeleton will be weaker and therefore, as extra precaution, the trilobite will hide in caves as a means of defence until a new exoskeleton has formed. When trilobites are juveniles or scavenging, they will often be immersed in other activities or are simply not fast enough to run from predators. Therefore the Asapiscus wheeleri hides in caves to protect its own wellbeing.
Perhaps the most likely environmental pressure which gave rise to this is the great number of prey which lurks in the oceans. As the Asapiscus wheeleri is a comparatively small creature, it may have been pressured to hide in murky and darker areas to protect it.
Behavioural Adaptation Two
Burrowing was another distinctive behaviour of the trilobite, similar to that of the hare. Although not all species did this, it is thought that the Asapiscus Wheeleri did because of its legs (underneath spine however not visible in fig. 01). Scientists are unsure however, there is evidence pointing to show that the Asapiscus Wheeleri dug burrows as a means of catching undersea worms and hiding from predators.
The environmental pressure which most likely led to this adaptation is the animal’s need to be competitive. As the Cambrian era was one of evolution explosion, there was great competition between different animals and therefore, the Asapiscus Wheeleri took to the ground to find food. In addition, hiding underground also came in handy when predators were on the chase. This could also explain the horseshoe crabs’ and the trilobites’ distinctively brownish murky colour.
Physiological Adaptation
One of the physiological adaptations to this animal is its gills which allow the Asapiscus Wheeleri to breathe underwater. Gills are an essential part of this aquatic animal because they are used to retrieve oxygen from the water in order for the animal to survive. They have gills which were different from that of sharks, which require constant water flowing through but instead had protection in order to be able to ‘swim’ when burrowing.
The most probable explanation leading to the development of the particular adaptation is that in order to become more competitive, the Asapiscus wheeleri had to be able to hunt food which lurked beneath the sea floor. In order to do that, it would mean that good gills would be essential for the animal and hence, there was an environmental pressure for this to develop.
Extinction Pressure
One of the major extinctions closely linked to the eventual disappearance of the Trilobite occurred later during the Ordovician Period. This is known in history as the “Ordovician Mass Extinction”. It is thought that a ice age began as a result of the drifting of Gondwana into the south pole region. As it moved slowly south, the trilobite followed and this eventually meant that the insufficiency of food, coupled with the inability to survive harsh and cold conditions would eventually kill off the trilobite. This is also an example of natural selection as the Horseshoe Crab had already begun evolving into its modern form during the time and is more adept at living in such harsh conditions. It meant that the Horseshoe Crab had more energy to scavenge for food and therefore, overtook the trilobite.
Trilobite, meaning three lobes or parts is currently the most likely ancestor of the Horseshoe crab. They are a series of hard shelled arthropods and in this case the species Asaphiscus wheeleri will be studied. This case study will attempt to explain the reasons behind the extinction of the Asapiscus wheeleri as well as its habitat and adaptations.
General Information
Scientific ClassificationHabitat
Cambrian was also a time when there was one of the most diverse amounts of trilobites, which accounted for almost half of all known hard-shelled marine creatures of the time. The Asaphiscus wheeleri fossils which have been located in the United States (Central) demonstrates as said before, the probable location of where the Asapiscus wheeleri lived.
The local flora of the sea was extremely diverse, with a great number of seaweeds and other aquatic plants. This meant that the brownish trilobite’s colour and its descendant, the horse-shoe crab, may have adapted to this murky colour as a means of protecting itself from predators. Apart from the flora, aquatic fauna was also at it’s height with a greatly diverse number of sea creatures including the trilobites diet, thought to be smaller crustaceans, molluscs and other species of Trilobite.
It can be said that their habitat animals is equal to that of the Horseshoe crab. However, unlike the Horseshoe crab, which has almost no predators, the Asaphiscus wheeleri was an extremely good lunch for animals such as the Laggania cambria (fig. 3) or even one of the largest sea creatures, the Eurypterid, ancient four metre sea scorpions.
During the Cambrian period, the temperatures would have generally been wetter and drier than today, meaning that there would have been more storms both on land and at sea. This may not have been exceptionally good for the trilobite Asapiscus wheeleri as it had a relatively small tail for balance. It could have meant that the Asapiscus wheeleri would be flipped over and easily devoured by other predators. This climate also meant most probably that the Trilobite, instead of depositing its young on land, composed of mostly barren desert, would have chosen the wetter marshes with large plantations of flora as camouflage.
Adaptations
Structural Adaptation OneCompared to the Horseshoe crab, the Asapiscus wheeleri had a heavier exoskeleton made from calcium minerals. This exoskeleton would require changing or replacement as the Trilobite grew and this process would involve splitting the exoskeleton through the head and thorax in a process called moulting. Such a heavy exoskeleton is most beneficial for the animal because of the great number of large predators which the Asapiscus wheeleri had to protect itself from.
The most likely environmental pressure which gave rise to a tough hard exoskeleton would have most likely been the great number of predators during the Cambrian age. Although it may have slowed down the swimming speed of the Asapiscus wheeleri, there must have been more chance of it surviving an attack due to its tough shell as a pose to outrunning the large predators. It is also thought that the earliest trilobites had a softer shell and, in an attempt to ensure survival, natural selection pushed for the development of this harder exoskeleton.
Structural Adaptation Two
Another structural adaptation of the Trilobite is the uniquely complex compound eyes. These complex compound eyes are extremely unique as there are no other known records of animal eyes composed from calcite. However, these eyes are similar to other animals such as cheetahs or other vertebrates. This is so because these compound eyes also have complex lenses which are able to detect colour and movement, unlike the Horseshoe crab. These eyes were thought to be used for three main purposes:
It is thought by scientists that this compound eye was conceived as a result of sudden rapid development of animals during the Cambrian age. As a result, this became an environmental pressure for animals to hunt with many competitors as well as run from many predators and therefore led to the development of these eyes.
Behavioural Adaptation One
A very interesting behaviour of the Trilobite is the fact that it sometimes hides in caverns when scavenging, a juvenile or moulting. The reason which scientist most attribute to this particular behaviour is that these are often times when the Asapiscus wheeleri is most vulnerable. When moulting, the exoskeleton will be weaker and therefore, as extra precaution, the trilobite will hide in caves as a means of defence until a new exoskeleton has formed. When trilobites are juveniles or scavenging, they will often be immersed in other activities or are simply not fast enough to run from predators. Therefore the Asapiscus wheeleri hides in caves to protect its own wellbeing.
Perhaps the most likely environmental pressure which gave rise to this is the great number of prey which lurks in the oceans. As the Asapiscus wheeleri is a comparatively small creature, it may have been pressured to hide in murky and darker areas to protect it.
Behavioural Adaptation Two
Burrowing was another distinctive behaviour of the trilobite, similar to that of the hare. Although not all species did this, it is thought that the Asapiscus Wheeleri did because of its legs (underneath spine however not visible in fig. 01). Scientists are unsure however, there is evidence pointing to show that the Asapiscus Wheeleri dug burrows as a means of catching undersea worms and hiding from predators.
The environmental pressure which most likely led to this adaptation is the animal’s need to be competitive. As the Cambrian era was one of evolution explosion, there was great competition between different animals and therefore, the Asapiscus Wheeleri took to the ground to find food. In addition, hiding underground also came in handy when predators were on the chase. This could also explain the horseshoe crabs’ and the trilobites’ distinctively brownish murky colour.
Physiological Adaptation
One of the physiological adaptations to this animal is its gills which allow the Asapiscus Wheeleri to breathe underwater. Gills are an essential part of this aquatic animal because they are used to retrieve oxygen from the water in order for the animal to survive. They have gills which were different from that of sharks, which require constant water flowing through but instead had protection in order to be able to ‘swim’ when burrowing.
The most probable explanation leading to the development of the particular adaptation is that in order to become more competitive, the Asapiscus wheeleri had to be able to hunt food which lurked beneath the sea floor. In order to do that, it would mean that good gills would be essential for the animal and hence, there was an environmental pressure for this to develop.
Extinction Pressure
One of the major extinctions closely linked to the eventual disappearance of the Trilobite occurred later during the Ordovician Period. This is known in history as the “Ordovician Mass Extinction”. It is thought that a ice age began as a result of the drifting of Gondwana into the south pole region. As it moved slowly south, the trilobite followed and this eventually meant that the insufficiency of food, coupled with the inability to survive harsh and cold conditions would eventually kill off the trilobite. This is also an example of natural selection as the Horseshoe Crab had already begun evolving into its modern form during the time and is more adept at living in such harsh conditions. It meant that the Horseshoe Crab had more energy to scavenge for food and therefore, overtook the trilobite.
References/Bibliography
Wikipedia. (2008). Trilobite. Retrieved 5th June 2008 from: http://en.wikipedia.org/wiki/Trilobite
Gon, S. (2008). Trilobites. Retrieved 6th June 2008 from: http://www.trilobites.info/
HSU Natural History Museum. (2008). Cambrian. Retrieved 6th June 2008 from: http://www.humboldt.edu/~natmus/lifeThroughTime/Cambrian.web/index.html
Gon, S. (n.d.). Asapiscus Wheeleri MEEK 1873. Retrieved 7th June 2008 from: http://pagesperso-orange.fr/jb.gayet/pages/anglais/Asaphiscuswhele.html
Wikipedia. (2008). Cambrian. Retrieved 8th June 2008 from: http://en.wikipedia.org/wiki/Cambrian
Kazlev, M. (2002). Cambrian. Retrieved 8th June 2008 from: http://www.palaeos.com/Paleozoic/Cambrian/Cambrian.htm
Chattern, B., Collins, D., Ludvisen, R. (2008). Cryptic Behaviour in Trilobites. Retrieved 9th June 2008 from: http://books.google.com.au/books?id=2E2fDXCkUEkC&pg=PA157&lpg=PA157&dq=trilobite+behaviour&source=web&ots=8W1wTxVBMT&sig=
P5zpfnmcSRDmfHnREsuLOTkSwB0&hl=en&sa=X&oi=book_result&resnum=2&ct=result#PPA157,M1
Schrantz, R. (n.d.). Research at KPS. Retrieved 10th June 2008 from: http://www.uky.edu/OtherOrgs/KPS/pages/research.html
Australian Museum. (2002). Palaeontology. Retrieved 10th June 2008 from: http://www.amonline.net.au/palaeontology/research/trilobites02.htm